The placement of a virtual machine that is built in a cloud service may change by the live migration. When a situation occurs that a virtual machine moves by the live migration to a physical machine that is subordinate to a router different from a router before the movement, a tunneling technique (for example, L2T Pv3 (Layer 2 Tunneling Protocol Version 3) and GRE (Generic Routing Encapsulation)) for encapsulating packets is used for the communication between virtual machines. A detailed example is illustrated in FIG. 1. In the example in FIG. 1, virtual machine 2 moves by the live migration to a physical machine that is subordinate to a different router. A layer-2 relay apparatus (gateway in FIG. 1) is placed subordinate to a router, and this gateway carries out the tunneling. As a result, a tunnel is formed between the gateways, so the communication is made possible between the virtual machine 1 and the virtual machine 2.
Incidentally, in the cloud service, in order to increase the availability of the service, redundant apparatuses may be provided. First, Virtual Router Redundancy Protocol (VRRP) that can be applied to layer-3 apparatuses is known as a method for controlling the redundancy of the routers. In VRRP, the redundancy is controlled by assigning an ACT (Active) or STBY (Standby) state to the routers, where a router that is in the ACT state transfers packets, and a router that is in the STBY state waits without transferring packets. However, in VRRP, it is possible to prepare plural VRRP groups, so it is possible to set routers that are in the ACT state for each VRRP group. For example, it is possible to carry out such settings that in VRRP group 1, router 1 is set to be in the ACT state, and the other routers are set to be in the STBY state, and in VRRP group 2, router 2 is set to be in the ACT state, and the other routers are set to be in the STBY state. Therefore, it is possible to efficiently use the routers.
On the other hand, Extreme Standby Router Protocol (ESRP) that can be applied to layer-2 apparatuses is known as a method for controlling the redundancy of gateways such as described above (in other words, layer-2 relay apparatuses that carry out the tunneling). In ESRP as well, the redundancy is controlled by assigning the ACT state or STBY state to each gateway, however, unlike VRRP, it is not possible to carry out control using plural groups. More specifically, when the gateway 1 is set to be in the ACT state, for example, the gateway 1 can transfer packets, however, all the gateways other than the gateway 1 are set to in the STBY state and cannot transfer packets.
Therefore, when the layer-2 apparatuses are redundant in a cloud service, there is a problem in that it is only possible to use the tunnel set for some layer-2 apparatuses, and routes for transferring packets are limited. There is also a problem in that the load is concentrated in some layer-2 apparatuses.
Conventionally, as for the redundancy and tunneling, there are techniques as follows. More specifically, plural Local Area Networks (LANs) are integrated into one Virtual Private Network (VPN) through IP networks using the tunneling technique. The redundancy is controlled by assigning virtual IP addresses that correspond to the connection destination LAN to both ends of each tunnel, and by correlating a group of routers with both ends of each tunnel. However, in this technique, the problem concerning the method of controlling the redundancy of the layer-2 apparatuses such as described above is not considered.
Namely, there is no conventional technique for efficiently transferring packets in case where the communication apparatuses are redundant.